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With the movement of the spoon you give energy to the particles and molecules.In this way the molecules increase their kinetic energy and many of them escape from the cup of the tea.Therefore the use of a spoon for cooling a cup of tea is valid!


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There are very few "fundamental" laws - everything else is ultimately derived from them. But let's look at Maxwell's equations just to see how tricky your question really is. Maxwell's equations are usually considered "fundamental" but they arrived after Ampère's law and Faraday's law - both of which describe "engineering principles" (magnetic field due ...


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Light years help give an idea of distances through space and time. When we look at a star 100 light years away, that 100 light years not only gives an idea of the immense distance to the object but will also tell us that what we see is light from 100 years in the past.


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Ultimately, the answer boils down to convenience. When we want to describe the distance between here and, for instance, the star Sirius (the brightest star in our night sky), it would be a little cumbersome to write $\ell=8.13\times10^{18}\,{\rm cm}$ any time we want to write its distance from us. And really this goes for any astronomical object: they're ...


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Whenever you see things at a distance, your perceptions are of things that happened in the past. You can see it at a football game, for example, where someone kicking the ball is seen very much before it is heard (sound is slower than light). Light only has a finite speed, too; and light turns out to be the fastest thing there is. A light year is the ...



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